Telegraph signaling apparatus



. April 1939- A. M. HUMBY 2,152,961

TELEGRAPH SIGNALING APPARATUS Filed April 18, 1935 3 Sheets-Sheet 1 Fig 1.

Filed April 18, 1935 5 Sheets-Sheet 2 Wr mm MMH 6 1L5-.. k will? April 4, 1939. A, M. HUMBY TELEGRAPH SIGNALING APPARATUS v 3 Sheets-Sheet 3 Filed April 18, 1935 Patented Apr. 4, 1939 UNITED STATES PATENT OFFICE water,

Application April 18,

England 1935, Serial No. 17,111

In Great Britain May 29; 1934.

9 Claims.

This invention relates to telegraph signaling apparatus and is particularly concerned with receiving apparatus for use in signaling in the code known as double current cable code. The invention relates to apparatus for receiving such signals in the ordinary way or to monitoring apparatus for producing a record of such received signals, or to apparatus for performing both of these functions. Generally speaking, of course, in receiving apparatus, perfectly formed signals are desired irrespective of the shape of the incoming impulses, while in monitoring apparatus, the record desired is usually an exact representation of the incoming signal impulses.

The signals employed in the double current cable code are produced by utilising two electrical conditions only which, for the sake of convenience, are usually referred to as marking and spacing. In ordinarytelegraphy, these are usually positive and negative currents, although they need not be and often would not be, particularly in wireless telegraphy using double currentcable code. The dot, dash and space signals are represented by causing the marking and spacing conditions to persist for different fractions of a complete signaling interval. The preferred system, and that which is generally used in practice, is as referred to in Patent 2,029,071 issued to Harry V. Higgitt, Jan. 28, 1936, among others and, in that system, a dot signal is represented by marking for 100 per cent of a signaling interval, a dash signal by spacing having a duration of 100 per cent of a signaling interval and a space signal is represented by marking for 50 per cent of a signaling interval followed by spacing for the other 50 per cent.

Signaling according to double current cable code has been received in a manner described, for example, in the above-mentioned Patent 2,029,071 by employing mechanical switching devices which in effect make contact on the spacing side at about a quarter of the way through each signaling interval and on the marking side about three-quarters of the way through each signaling interval. If space signals are received the circuits so prepared are never completed. If a dot signal is received, circuits allocated. to dot signals are completed at a point threequarters of the way through the signal interval. If a dash signal is receivedthe circuits allocated -to dash signals are completed at about a quarter the way through the signal interval. Clearly, similar mechanical contact-making devices, including a vibrating reed, a phonic motor driving cam-operated contacts and the necessary relays could be used for monitoring or recording signals in this way, the record appearing as a distorted cable code signal because of the circuits being completed in the first half of a signaling interval for a dash signal and in the second half of the signaling interval for a dot signal. This distortion is not a serious drawback in practice, but this form of monitoring device has one serious disadvantage, especially when used in a radio receiving station because the make-and-break 10 contacts and "their associated circuits, unless special precautions are taken, radiate disturbances setting up a high-noise level. It is well known that unless the noise level is reduced to an absolute mini-mum, the reception of radio tele- 16 graph signals may be severally impaired during periods of low field strength.

The channels A and B referred to herein cor respond to the channels so identified in the patent referred to above.

The object of the invention is to provide a receiving device for double current cable code and particularly a monitor-ing or recording device which provides a cable code record while reducing the num'ber of make-and-break contacts and consequen'tlythe noise level to a minimum. Theinvent'ion further aims at providing low initial and maintenance costs; reliable operation and the possibility of easy adjustment for receiving signals at dilferent centrehole speeds. Incidentally, the invention can be arranged to provide an apparatus which avoidsthe distortion due to selecting the dot and dash signals at different parts of the signal interval;

According to the present invention, an oscillating. discharge tube circuit is employed tuned or adjusted toa frequency to suit the centre-hole speed of the signals-to be received or monitored; this oscillating circuit is employed to control the operation of a circuit controllingdevice .such as a :relay so that its tongue closes different contacts at channel speed when there are two or more charmels tolbe received. This. operation is independent of the position of the tongue of the signal input relay and is. arranged to control the action-of a pair of electron discharge tubeswhich control a cable code undulator in such a way that these tubes are subject to the action of the signal input :rel'ay only during the periods of reception: on the, channel which it isdesired to monitor. During the remainingperiods, the said tubes are rendered non-conductive so that no recordzis-obtained. In the case of .a two-channel system, by means of a channel selector switch the apparatus may be set to produce a record of either channel at will, or if desired the arrangement may be so made that the oscillatory discharge tube circuit controls alternately apparatus belonging to the two channels so that both channels may be monitored. It is not found in practice, however, that the necessity for a simultaneous check on both channels often arises. It is found to be better to direct attention to one channel only since a defective radio or control link is common to both channels. Generally speaking, if a channel can be selected at will as, for example, by a channel selector switch as mentioned above, the provision for simultaneous check on both channels turns out to be an unnecessary complication.

In practical working, it is found convenient to adjust the thermionic oscillator to oscillate at a frequency very slightly below the signaling frequency and to correct the phase relationship by means of a negative impulse applied to the grid or grids of the tube or tubes of the oscillatory circuit at the instants that the signal input relay I tongue reverses from spacing to marking. This is provided for by arranging for the signal input relay at those instants to apply a negative impulse from the battery through condensers to the grid or grids of the tube or tubes in the oscillatory circuit. 7

In order that the invention may be clearly understood and readily carried into efiect, two examples of monitoring systems in accordance with the present invention will now be more fully described with reference to the accompanying drawings, in which Figure l is a diagram of connections of a monitoring apparatus according to the invention in which the signals on either channel of two channels can be checked at any one time;

Figures 2 to 5 are a series of diagrams illustrat- ;ing in detail the timing of the different parts of the system shown in Figure 1; and

Figure 6 is a diagram of connections of a modified system to enable the signals on two channels to be checked at the same time.

Referring first of all to Figure 1, two resistancecoupled discharge tubes V V connected in pushpull are employed to form a multi-vibrator circuit. The grid circuits include resistances r 1 in. both branches as does the divided anode circuit where the resistances are marked R R The junction point between the grid resistances r 1' is joined through a variable resistance R the tapping point of which is connected to the battery B and may be connected, for example, at

a point eighteen volts from the positive end of that, battery, the battery having a total voltage of 108 volts. The frequency of oscillation of the multi-vibrator tubes V V is adjusted by varying the tapping point on the resistance R The two grids of the tubes V V are also cross-connected through condensers C C each being connected through its condenser to the anode of the opposite tube in the ordinary fashion. The anodes of both tubes are connected at the junction point of the resistances R R to the positive terminal of a 220 volt battery B through a decoupling combination of a series resistance a and a shunt condenser b.

The grids of the tubes V V are connected by .means of conductors I, 2 directly to the grids of a pair of amplifying tubes V V These tubes have divided anode circuits passing through the differential windings w w of a relay CR, the anode circuit being completed through a resistance d to the positive pole of the anode battery B The anode circuit of the tube V includes a milliammeter 3 for the purpose which will be described below. The tongue 4. of the relay CR is arranged to control the operation of a pair of recording tubes V V the output circuits of which control a cable code undulator or moving coil recorder U. The tube V has its grid connected direct to the tongue 4 of the relay CR. The grid of the tube V is connected to a switch 5 which, when it is on its upper contact 6, connects the grid of the tube V to the marking contact m of relay CR. When the switch 5 is on its lower contact 'I on the other hand, it connects the grid to the spacing contact 8 of the relay CR.

The receiving relay RR has its tongue 8 connected to the negative pole of the battery B which, when the relay is in the marking position, comes into contact with the contact m and connects the battery B to the grid of tube V. Similarly, whenthe relay RR is in the spacing position, the'tongue 8 and the spacing contact 8 connect the battery B to the grid of the tube V There is a connection 9 through a condenser e from the marking contact m to the divided grid circuits of the tubes V and V intended, as will be described below, to keep the vibrating tubes V and V in step with the receiving relay RR. Resistances X and Y, which preferably are small and may sometimes be entirely omitted, are shown included in the grid leads to the tubes V and V in order to avoid any risk of mis-phasing of the multivibrator circuits during the initial setting up of the apparatus; such an effect might otherwise result due to correction impulses from the spacing contact s through the condensers C and C In considering the operation of this system, it will be assumed that one of the channels, which may be referred to as the B channel, is to be checked and, for that purpose, the channel selector switch 5 is placed on its contact 6 so as to connect the grid of the tube V to the marking contact m of the channel relay CR. The grids of the tubes V V are connected to ground through condensers C and the resistances R R across these condensers. The resistances X and Y being relatively small, when the relay CR closes on its marking contact m it connects the grids of the tubes V V together and since the relay RR is always closed at one or the other of its contacts m, s the condensers C C are charged substantially to the voltage of the battery B say 108 volts, that is to say, the grids of these two tubes V V receive a negative charge beyond the cut off grid potential of the tubes so that the two recording tubes are maintained non-conductive. In fact, the relay OR is timed so that the tubes are thus rendered non-conductive at the commencement of each channel interval on the A channel and they remain in that condition during each A channel signaling interval. During these intervals, therefore, there is a zero output to the cable code undulator U.

In order to make this clearer, reference will be made to Figures 2 to 5 of the drawings. Figure 2 is intended to represent incoming signals, that is to say, the upper amplitudes of the curve represent closing of the receiving relay RR on its marking contact and the lower amplitudes closing of that relay on its spacing contact. The parts of thecurve in full lines represent signals on channel A and the parts of the curve in dotted line represent signals on channel B. Therefore in Figure 2, bearing in mind, as already stated, that a dot signal is represented by marking for area-ass 100. per: cent of a signaling; interval, dot signals on. the: in channel are: shown: im Figure. 2. at. Ill

and: I I. and: similarly dot signals are? shown comingin.onzthelBschanneliati l2.;.l3; M. Then again a dash: si'gnalfiis represented: byspacing having a.- duration: of. 100 per cent; of; a signaling. interval.

sozthat. iniFigure. 2fdashes arriving on :the Achannel; are; shownzat 15,-. lifii and: onxther B? channel at H. Finally a space signal is represented by marking for. 5.0. per cent of. a. signaling interval,

followed. by. spacingv for the other: 50. per cent.

Thus, space signals are: indicated; in Figure 2. as

arriving: om the'A channeliati. I8, I 9; 20: and 21 and on the B channel at 22, 23 andJZl. It may be. assumed incFigurez thatathespeed ofsignaling is represented: by." 3000. centre holes per minuteso' that as channel. signaling interval represented:

for example by the distance t" is. equal to one-- fiftieth of. a second. The actual vertical lines in Figure 2; of course; represent the points of change-over: of" the tongue 8 of" the receiving relay RR.

Figure: 4 is intended to; represent the record which will be obtained on the B channel when the signals shown in Figure Z arrive. As already' m'entioned the relay CR is timed so that the tubes V and V are rendered non-conductive at the commencement of each channel interval on the A channel, that is-to sayg atthe instants of time marked 25:, 26'', 27, 28, 29*, 30; 34 32. It follows from. what has been said that at those instants of time the relay: tongue 4 passes on to the marking contact m This is represented in Figure S Qf-the-draW-ings where again thepositive ordinates represent the time of" contact on the marking contact m and; the negative ordinatesrepresent the time of contact on the spacing contact s It willbe noted also from Figure 5 that the speed of reversal of the channel relay CR is 1500 centre holes-per minute.

As explained above, during each A channel signaling interval, the'fact that the relay'CR is on its -m'arkingcontact 722 as indicated by the full linesin Figure 5, means that during the A channel int'ervals there is no output to the undulatorU'. Therefore in Figure 4, which shows the record of the signals arriving on theB channel, it will be noted that during the'A channel signaling intervals the record is at zero.

However, during an aggregate signaling interval following that: referred to and therefore during the signaling interval on the B channel, the relay tongue 4 istaken off the marking contact m on to the spacing contact 8 as indicated by athe dotted lines in Figure 5. The result is that the grids ofthe twotubes V V are then controlled only by the tongue 8- of the signal input relay RR. Suppose now a dot signal comes in on the B channel, such as indicated at 12, I3 or M 3.0; in Figure 2, this means that the tongue 8 01' the relay RR remains on the marking contact m during the whole of the signaling interval on the B channel, so that the negative pole of the battery B is connected to the grid of the tube V for example during'the whole of the signaling interval 33, 28 on the B channel. Consequently the tube V remains non-conductive during the whole of this signaling interval 33, 28. However, the

grid of the tube V is not connected to the- 70iinegative of the battery B but its grid charge 755 the latter willcommence to. conduct; The delay due; to. the: time? period of-f the. circuit C R is adjusted to; be equal1to: half of one signaling period... Therefore, duringrthe first. half of the signaling period; 33,3281. the; tube V remains nonconductive and there isanorecord on the B channel: as: indicated at.3d'.in Figure 4. However, for the:- reasons just; stated during the second half of: the.signaling:periodt33, 285 current will flow in theanode?circuiti'of;theitubev from the positive pole. of? battery Bi through. the conductor 35, througlii the. output. resistance R, through the tube'v to" ground. Consequently, there is a fall of potential? in. the resistance; R, the upper end beingmore positive, with. the result that the recording current. flows downwards through the undulat'or U2. This: produces. a. record shown at 36:in Figure 4; and; ofz'course, the same kind of record; is. obtained? for the. dots l3, M as shown at 311*; 381

If, during anothersignaling interval on the B channel, a dash signal arri-veasuch as shown at H in: Figure 2; itwill be" seen from what has been said above that the signaling input relay tongue 8f will remain. on its spacing contact 8 for the whole of 'thesignaling interval. Consequently the tubefifl in this=case willremain nonconductive for the whole signaling. interval, but the tube V will become conductive half way throughthe signaling interval. In this case, therefore, anode. current: will flowfrom the conductor" upwards through i the output resistance P through-the tube. v 'toground Therefore there is a drop of potential in the resistance P, its lower end being more positive than its upper end so that current will flowthrough the undulator U but this time upwards. The result is as shown" in Figure 4 at 39 the record of a dash is provided.

Yet again, if a space signal is-received during a signal intervalonthe B channel, as for example is the casein thesignal 23 in Figure 2, it followsthat during thefirst half of the signaling interval the relay tongue 8 will be on the marking contact 1n and for the other half of the signal; onthespacingcontact s, but as both the circuits- R (2 andR C have a time period providing a delay of half a signal period, it is clearthat neither of the tubes are allowed to become conductive in the-signal interval in question so that there is no output to the undulator U as-indicated' at 40" in-Figure' i. It will be noticed from Figure 4 that" by means of the apparatus described, the dot and dash elements on the cable coderecord'asse'en at 39, 36, 31, 38'are correctly spaced becauseas can be clearly seen-each element of the record is produced during the second half ofacorresponding-signal interval.

It" is clear bychanging'over the channel selector switch 5'- tothe contact" 1 that a similar record can be obtained on-theA channel. There is no needto gothrough this'in detail as the action is exactly the sameas that described for Figure 4 on the B channel, but in- Figured the dot signals Hl'and l'l' are-shown recorded at M and t2 and the dash signals at I5 and I6 are shown recorded at 43 and M";

It should be appreciated that the arrangement of the system requires that the signal input relay tongue 8 shall always change over from the-spacing contact 8 to the marking contact" matthe same instant that the channel relay tongue 4 passes over: It can readily be appreciated-2 from" Figures 2 and 5 that this condition is fulfilled; 'I'hus, Figure 2, as already pointed out,. represents; the; change-over of the tongue 8 and it can be seen that this tongue changes over from spacing to marking at the instants of time indicated at 25, 45, 26, 33, 46, 41, 3|, 48. It will be noted in Figure 5 that at these same instants of time the channel relay tongue 4 changes over. -In the actual system, this may be ensured by adjusting the multivibr ator circuit by shifting the tapping on the resistance R to a frequency very slightly below the synchronous signal frequency and by restoring the phase relationship by impressing upon the grids of both tubes V and V a negative impulse with respect to ground at the instants that the signal input relay tongue 8 changes from spacing contact 8 to marking contact m. This is the purpose of the connection 9 and it ensures that at the instant when the tongue 8 goes over to the marking contact mthere is a negative charging impulse from the battery B through the condenser e to the grid condensers C C which pulses the grids of the tubes V V to the same negative potential to produce the desired result.

If the oscillatory circuit is in synchronism there is a steady anode current indicated by the instrument 3 when the double current cable code signal input is applied, then the resistance R is slightly increased so that the frequency of the oscillatory circuit is made very slightly .below the synchronous signal frequency. If this is effected when the battery B is fully charged, the small reduction in frequency due to discharge of the battery is not sufficient to make it necessary to readjust.

The system also allows a quick change-over from one station to another. Thus, in practice transmissions may have to be received of which the aggregate speed is 3000 centre holes per minute as already indicated with reference to Figures 2 to 5, or again 2718 centre holes per minute. In the former case the frequency of the multivibrator circuit is 25 cycles per second and in the latter case the frequency is 22.65 cycles per second. However, the change can readily be made by adjusting the resistance R The tapping point 49 in the battery B? may be shifted and this provides a simple means of obtaining the desired time delay in the tubes V V becoming conductive for any given speed of signaling.

Figure 6 shows a slight development of the system according to Figure 1 arranged for enabling a simultaneous check on both channels of a two channel system to be provided. In Figure 6 the circuits of the oscillator tubes V V and the circuits of the relay tubes V V are exactly the same as in Figure l and these tubes are common to both channels. However, the two channels are provided with their own pair of recording tubes, the tubes WA and V A being associated with the A channel and the tubes V 3 and WE with the B channel. Each channel has its own undulator UA, UB.

It will also be noted that the channel relay CR has duplicate contacts and, in fact, in its marking position the tongue 4 bridges contacts m m and in the spacing position, it bridges contacts s s while the channel selecting switch 5, 6, l is omitted. The contacts m m are connected to the grids of the tubes V A, V A, while the contacts s and s are connected to the grids of the tubes V 13 and V B. Furthermore, the signal input relay RR is arranged for its tongue 8 to co-operate with two contacts m m when in the marking position, and with, two

contacts s s when in the spacing position. The result is that the tongue 8 in either of its positions connects the negative terminal of the battery B in the one case to the grids of the tubes WA and WB, and in the other case, to the grids of the tubes V A and V 13. As before, the phase or time correcting impulses are led from one of the marking contacts of the relay RR, viz., the contact m through the condenser e by way of the conductor 9 to the junction point of the condensers C C The remaining parts of the circuits are connected exactly as in Figure 1 and the same referencecharacters have been employed.

As regards the operation of the system shown in Figure 6 it is clear that when signals on the B channel are arriving, the recording tubes V and V belonging to the A channel are not conductive whatever signals are received on the A channel because the tongue 4 of the relay CR connects together the contacts m and m and the tubes V and V are entirely under the control of the tongue 8 of the signal input relay RR. The operation therefore is precisely similar to that described in detail in Figure 1, except that each record is formed when, in any event, the recorder on the other channel would not be operative.

The apparatus described and illustrated produces a record which is a faithful copy of the incoming signals and shows any distortion or mutilation. When the apparatus is used for monitoring or checking purposes this is, of course, the result desired, but when the circuits are used for ordinary reception of signals it is more important to produce signals of good shape free from distortion. Such a result can be obtained by introducing. a relay between the recording tubes V and V and the undulator U. Yet again, the shape of the signals can be improved for reception purposes by inserting a battery in the lead to the cathodes of the tubes V and V from the junction of the resistances R and R soas to introduce a positive bias voltage on the grids of these two tubes. Owing to the effect of grid current, the tubes will operate between points on their characteristic curves which are less sensitive to malformation in the incoming signals. I

I claim:

1. In a telegraph signaling apparatus for receiving or recording double-currrent cable code signals employing three kinds of signals constituted by two different electrical conditions per sisting for different portions of a signaling period, the combination of a signal input relay, a pair of electron discharge tubes connected to the contacts of said relay so as to be subjected to the incoming signals, a source of electrical supply and a further relay having contacts actuated in synchronism with the incoming speed of the signals to connect said source to render said tubes non-conducting except during the periods of arrival of desired signals.

2. In a telegraph signaling apparatus for receiving or recording double-current cable code signals employing three kinds of signals constituted by two different electrical conditions persisting for different portions of a signaling period, the combination of a signal input relay, a pair of electron discharge tubes connected to the contacts of said relay so as to be subjected to the incoming signals, a signal recording instrumentconnected to the output electrodes of said tubes, an oscillatory electron discharge tube-circuit adjusted to a frequency to suit the speed of arrival of the signals, a source of electrical supply and a further relay energised from said oscillatory circuit and having contacts connected to said source through contacts of said signal input relay and to said electron discharge tubes to render the latter non-conducting except during the periods of arrival of desired signals.

3. In a telegraph signaling apparatus for receiving or recording double-current cable code signals employing three kinds of signals constituted by two different electrical conditions persisting for different portions of a signaling period of which two of the kinds of signal are represented by the two difierent electrical conditions each persisting for a complete signal period, the combination of a signal input relay, a pair of electron discharge tubes each connected to the contacts of said signal input relay so as to be controlled in accordance with the incoming signals, a further relay having contacts actuated in synchronism with the speed of the incoming signals and connected so as to connect the inputs of said tubes together periodically and to one contact of said signal input relay, and a source of electrical supply so connected to the tongue of said signal input relay as to enable said signal input relay in conjunction with said further relay to render both of said tubes non-conducting except during the periods of arrival of desired signals.

4. In a telegraph signaling apparatus for receiving or recording double-current cable code signals employing three kinds of signals constitued by two different electricalconditions persisting for different portions of a signaling period of which two of the kinds of signal are represented by the two different electrical conditions each persisting for a complete signal period, the combination of a signal input relay, a pair of electron discharge tubes each connected to the contacts of said signal input relay so as to be controlled in accordance with the incoming signals, a further relay having contacts actuated in synchronism with the speed of the incoming signals and organised so as to connect the inputs of said tubes together periodically and to one contact of said signal input relay, and a source of electrical supply connected to the tongue of said signal input relay so as to enable said signal input relay in conjunction with said further relay to render both of said tubes non-conducting when the'inputs of said tubes are connected together by said further relay and, at other times, said relays maintaining one only of the tubes nonconducting and allowing the other of said tubes to be restored to the conducting state.

5. In a telegraph signaling apparatus for receiving or recording double-current cable code signals employing three kinds of signals constituted by two different electrical conditions persisting for different portions of a signaling period of which two of the kinds of signal are represented by the two different electrical condi tions each persisting for a complete signal period, the combination of a signal input relay, a pair of electron discharge tubes each comprising an an ode, a cathode and a grid, the grid of each of said tubes being connected to said signal input relay so as to be controlled in accordance with the incoming signals, a further relay having contacts actuated in synchronism with the speed of the incoming signals and organised so as to connect the grids of said tubes together periodically and to connect both of said grids to one contact of said signal input relay, and a source of electrical supply so connected to the tongue of said signal input relay that when the grids of said tubes are connected together by said further relay and said signal input relay closes on the said contact, the grids of the said tubes are rendered sufficiently negative to render both of said tubes non-conducting while at other times said relays maintain only one of said tubes non-conducting, said other tube being restored to its conducting state.

6. In a telegraph signaling apparatus for receiving or recording double-current cable code signals employing three kinds of signals constituted by two different electrical conditions persisting for different portions of a signaling period of which two of the kinds of signal are represented by the two different electrical conditions each persisting for a complete signal period, the combination of a signal input relay, a pair of electron discharge tubes each comprising an anode, a cathode and a grid, the grid of each of said tubes being connected to said signal input relay so as to be controlled in accordance with the incoming signals, a further relay having contacts actuated in synchronism with the speed of the incoming signals and organised so as to connect the grids of said tubes together periodically and to connect both of said grids to one contact of said signal input relay, a source of electrical supply so connected to the tongue of said signal input relay that when the grids of said tubes are connected together by said further relay and said signal input relay closes on the said contact, the grids of the said tubes are rendered sufficiently negative to render both of said tubes non-conducting while at other times said relays maintain only one of said tubes non-conducting, said other tube being restored to its conducting state, and a condenser shunted by a resistance connected to the grids of each of said tubes to allow said grids to discharge and render the respective tubes conducting when freed from the control of said signal input relay.

7. In a telegraph signaling apparatus for use in double-channel working for receiving or recording double-current cable code signals employing three kinds of signals constituted by two difierent electrical conditions persisting for different portions of a signaling period, the combination of a pair of electron discharge tubes connected to be subjected to the incoming signals, a source of electrical supply, a relay comprising a tongue and opposite contacts actuated at channel speed, said tongue being connected to the input of one of said tubes and a manually-operated switch connected so that in alternative positions it connects the input of the other tube to one or other of the opposite contacts of said relay,

8. In a telegraph signaling apparatus for receiving or recording double-current cable code signals employing three kinds of signals constituted by two different electrical conditions persisting for different portions of a signaling period, the combination of a circuit controlling device, a signal recording instrument connected to be under the control of said circuit controlling device, a signal input relay, an oscillatory electron discharge tube circuit adjusted to a frequency to suit the speed of arrival of the signals and connected to control the operation of said circuit controlling device so as to cause current to flow to said recording instrument only during the periods of arrival of desired signals and a connection from said signal input relay to said oscillatory electron discharge tube circuit for conveying correcting impulses to said circuit in step with the changing-over of said signal input relay.

9. In a telegraph signaling apparatus for receiving or recording double-current cable code signals employing three kinds of signals constituted by two different electrical conditions persisting for different portions of a signaling period, the combination of a signal input relay, a pair of electron discharge tubes connected to the contacts of said relay so as to be subjected to the incoming signals, a signal recording instrument connected to the output electrodes of said tubes,

an oscillatory electron discharge tube circuit adjusted to a frequency to suit the speed of arrival of the signals, a source of electrical supply, a further relay energised from said oscillatory circuit and having its contacts connected to said source of supply and to said electron discharge tubes to render the latter non-conducting except during the periods of arrival of desired signals and a connection from said signal input relay to said oscillatory electron discharge tube circuit so as to convey correcting impulses to said circuit in step with the changing-over of said signal input relay.

ALBERT MAURICE HUMBY. 

